1. Field of the Invention
The present invention relates to an apparatus and method for transporting and agitating a substance having solid and liquid constituents.
2. Description of Related Art
Many industrial processes require raw materials consisting of solid and liquid mixtures. For example mixtures, such as calcium carbonate in water or clay water slurries, are extremely difficult to transport and store because dense solid materials settle on the bottom of storage containers during transportation and/or storage. When the container is drained the liquid portion of the mixture is readily removed, but a portion of the solid sediment remains in the storage container. Thus it is difficult to completely unload all of the solid material.
Calcium carbonate is a substance used as a component in a number of common household medical products such as antacid and toothpaste. Additionally, the paper industry uses this material as a substitute for wood pulp paper filler to eliminate the need for unnecessary destruction of forestry. Because of the great demand for the end products produced by these industries, extremely large quantities of calcium carbonate must be transported.
Calcium carbonate is mined from the earth in large boulders, and crushed to create a fine powder substance. This powder is then normally mixed with water to create a solid and liquid suspension that is relatively easy to handle. The calcium carbonate and water mixture is loaded in transportation devices, such as railroad tank cars for shipping.
While the solid and liquid mixture is within the tank of a transportation device, the calcium carbonate solid material settles in the liquid and gradually forms a sediment on the bottom of the tank. This solid sediment is extremely difficult to remove from the tank when the tank is unloaded. The retention of solids in the bottom of the tank poses numerous disadvantages. First, the backhaul of the tank to pick up another load requires unnecessary rehauling of the solids back to the original pickup point, making the tank heavier and wasting fuel. Additionally, the build-up of solids reduces the capacity of the tank so that each subsequent refill of the tank includes less and less volume. Therefore it is desirous to remove all of the settled solid material along with the liquid when the mixture is unloaded. This removal process, however, is normally an extremely time consuming and expensive process.
Some previous attempts to deal with this problem have met with limited success. In one removal process, a worker introduces a pressurized air hose through the opening of a tank and passes the open end of the hose along the bottom of the tank. The pressurized air circulates through the solid material to mix the solid with the liquid. This process is extremely inefficient, because a worker is required to pass the open end of the hose along the entire bottom surface of the tank in a time consuming procedure.
Additionally, sparger systems have been used on tank cars to recirculate a substance within a tank. These systems include a pipe positioned along the floor of a tank and having small holes along its length. This pipe is either connected to a source of compressed air or a fluid pump. When the product within the tank is nonflammable, the tank is vented and the compressed air is blown in the pipe to emit air bubbles from the holes for mixing the products in the tank. If a flammable product is within the tank, the material is recirculated in the tank by pumping liquid from the top of the tank into the pipe and allowing the liquid to flow through the holes into the bottom of the tank. These sparger systems have met with limited success, because settled solid material is not adequately mixed unless it is an extremely lightweight powder. Further, the small holes in the pipe are prone to clogging with solid material that has settled in the tank.
Because many of the current means for unloading solid and liquid mixtures are time consuming, large storage tanks having agitators are required at destination sites. These storage tanks maintain solid and liquid materials in a mixture form for immediate use in an industrial process, however, these on-site tanks could be eliminated if a solid and liquid mixture was able to be immediately unloaded from a transportation tank.
U.S. Pat. No. 1,652,960 to Snelling et al. discloses a tank for transporting materials along a railway. This tank has a series of rotatable agitating blades mounted to vertical shafts that extend through a top wall of the tank. These shafts are rotated by a horizontal drive shaft that is positioned on the tank exterior and connected to a belt pulley. Because the vertical shafts extend through a wall of the tank, complicated drive connections, bearings and seals are required. Additionally, it is often important to pressurize the vessel to facilitate unloading. However, because the shafts pass through the tank wall, it would be difficult if not impossible to comply certain Department of Transportation regulations as well as the American Society of Mechanical Engineers' pressure vessel standards.